How Power Plants Work

Background

There
are many different types of power plant technologies, each with
positive and negative aspects. Here we explore some conventional power
plant types: coal (where CO2 is released), coal (where CO2 is captured),
coal-to-gas (where CO2 is released), coal-to-gas (where CO2 is
captured), wind, natural gas, nuclear, solar cell, energy efficiency,
and biomass-and-coal.

In coal power plants where CO2 is released,
the coal is burned to create steam. The steam powers a turbine, which
in turn runs a generator, producing electricity. As the coal is burned,
it releases CO2 into the air. While coal plants are steady and reliable,
they release a lot of CO2into the atmosphere and produce a lot of
solid waste in the form of ash. Coal mining also negatively impacts the
environment by disturbing the land and potentially polluting streams. In
addition, while coal plants are safe for operation, the coal mining is
still dangerous today.

In coal power plants where CO2 is
captured, the plant produces electricity the same way as a coal power
plant where CO2 is released. However, there is additional equipment to
convert the CO2 into a liquid and transport it to rock formations, where
the liquid CO2 will be trapped. While this decreases the release of CO2 into the atmosphere, there is a small chance that CO2 can contaminate
underground drinking water. In addition, there are also very small risks
of CO2 leaks and very small risks of earthquakes occurring as a result
of the increase in pressure.

Coal-to-gas power plants (where CO2 is released) use the heat from the burning of coal into gas to power a
turbine. The turbine then runs a generator to produce electricity. The
burning of coal to gas also provides heat to make steam, which is used
to power a second turbine. Because coal-to-gas power plants have two
turbines, they are more efficient than the previously mentioned coal
power plants. While coal-to-gas power plants release less CO2 than coal
power plants, they release similar amounts of solid waste and also
require coal mining.

Coal-to-gas power plants can also have
capture equipment to reduce air pollution from the release of CO2. This
capture equipment is a little better than coal power plants with CO2 capture, but work in the same way. CO2 is converted to liquid and stored
over 2500 feet underground. The risks are the same as those for
coal-to-gas power plants where CO2 is released, and for coal power
plants where CO2 is captured.

Natural gas power plants work
similarly to coal-to-gas power plants. The gas is burned, and the heat
from the gas is used to power a turbine. The turbine runs a generator,
producing electricity. The hot gas also makes steam, which is used to
power a second turbine and a second generator. Natural gas can either be
found in conventional sources or unconventional sources. Conventional
natural gas is found in sandstone and other sponge-like layers of rock,
while unconventional natural gas can be found trapped in shale deep
underground. Unconventional natural gas can be extracted with methods
such as horizontal drilling, where a vertical well is drilled, followed
by a hole drilled sideways. A salty water solution is then pushed
through the well, causing the rock to break up as the result of high
pressure and releasing the gas to the surface. While natural gas still
releases CO2 into the atmosphere, it is about half that of a coal power
plant, and doesn’t release any solid waste. However, drilling for
unconventional natural gas is controversial, and may disturb local
plants, animals, and water supplies.

Nuclear power plants require
enriched uranium atoms. These atoms are split to release heat, which
powers a turbine that runs a generator, creating electricity. Many
people worry about the safety of nuclear power plants. However, the
chance of a nuclear accident is very small, and the plants release
almost no radiation into the ground, air, and water. The waste from
nuclear plants will emit radiation, but storage technology should keep
the waste safe for up to thousands of years. Nuclear technology built in
the future will be even safer than the already safe design as well.

Two
well-known equations govern power. Ohm’s Law states the voltage (V) is
equal to the product of the current (I) and resistance (R), or:

V=I*R

and the power (P) is equal to the product of the voltage and the current, or:

P=V*I=R*I^2

Additionally,
Kirchoff’s Current Law states that all currents into a node sum to
zero, and Kirchoff’s Voltage Law states that all voltages in a loop sum
to zero.

Objectives

Students will be able to:

Describe what the most common fuels used in conventional power plants are

Understand how power plants generate electricity through boiling water and spinning a turbine. They should also understand the concept that spinning an object can produce electricity (even if they don’t know the physics behind it).

Burning fuel to produce electricity is inefficient.

The relative greenhouse gas emissions from coal and natural gas power plants.

Materials Needed

Safety Concerns

None.

Vocabulary

Power: describes how much energy can be produced in a given time. Also to supply a device with electricity; the product of voltage and current. A common unit of measurement is a watt (W); also measured in watts, kilowatts, megawatts, etc.

Energy (general): Energy that the plants and animals originally obtained from the sun is stored in the form of carbon in natural gas. Also the capacity of something to do work; an amount. Measured in watt-hours, kilowatt-hours, megawatt-hours. A typical American household used 940 kWh per month in 2011.

Voltage: the difference in the electric charge of two places. A common unit of measurement is a volts (V).

Current: flow of electric charge, or the flow of electrons. A common unit of measurement is an ampere, or amp (A).

Resistance: a material’s opposition to electric current. A common unit of measurement is an ohm (Ω).

Procedure

Activity 1: Introduction

Time: 15 minutes

Description

Group discussion:

Where does electricity come from? Describe conventional power
plants, what fuels are used (pass around coal and can of natural gas).

Activity 2: Pinwheel Experiment

Time: 25 minutes

Supplies: Pinwheels

Description

Have students break into groups.

Let students play around with pinwheels, finding right angle to blow in order to get them spinning fast.

Have students hold two pinwheels in line and blow such that they
both spin. Observe speed of second (downwind) pinwheel. Remove first
pinwheel and observe change in speed in second.

Why does this occur?

Is all of the energy in your breath converted into rotational energy of pinwheel?

How could you increase the fraction of breath energy converted into rotational energy?

What is efficiency and how does it relate to what we have just done?

Activity 3: Teacher Demonstration

Time: 5 minutes

Supplies: Hot pot burner, pinwheel, stand

Description

Boil water and spin a pinwheel. Describe that this is what happens inside a power plant. Promote group discussion.

The
Emirates Nuclear Energy Corporation gives a succinct summary of how
nuclear power works with an accompanying video to demonstrate the
process. Teachers looking for a reputable source to explain the basics
behind nuclear power could look here.

This
EPA page gives a summary on what natural gas is, what natural gas is
used for, and how it’s used to generate power. If a teacher wanted to
get a better background on natural gas, this would be a good place to
start looking.

The
Coal Can Do That page talks about the benefits and process of
converting coal into either a liquid or a gas. Though it is clearly
biased, teachers looking to introduce the process of gasification could
look here.

The
International Risk Governance Council primarily links to a research
paper from Edward Rubin that discusses Carbon Capture and Sequestration
technology. However, it also gives a brief summary of what it is, and
how the IRGC approached the research. Teachers ultimately looking for an
incredibly detailed summary of CCS – from the research paper – could
look here.

Because
of increasingly strict emissions standards, NRG Energy plans to convert
their coal power plant to natural gas. The article gives some
statistics on how many power plants NRG Energy has, what the estimated
cost of the switch may be, and how power generation will differ.
Teachers looking for a current event on why the topic is relevant could
look here.

The
World Coal Association page on coal power plants – while biased in
favor of coal – provides statistics on coal usage globally, provides a
helpful diagram of what a power plant consists of, and talks about
recent improvements in efficiency. Teachers looking to highlight some of
the positive aspects of coal power plants could look here.

Author(s)

Lesson
idea from Andrew Hamann; final product compiled by Kelly Klima on
behalf of the Leonard Gelfand Center for Service Learning and Outreach.

Funding Sources

Portions
of this work were supported by a) the Leonard Gelfand Center for
Service Learning and Outreach, and b) the Center for Climate and Energy
Decision Making (SES-0949710) through a cooperative agreement between
the National Science Foundation and Carnegie Mellon University.

Next Generation Science Standards Alignment

HS-PS3-3: Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.

Crosscutting Concept: Influence of Science, Engineering and Technology on Society and the Natural World

PS3.A: Definitions of EnergyPS3.B Conservation of Energy and Energy Transfer